Electrostatic precipitators which use a plurality of electrodes to remove particulate matter must be cleaned periodically during operation if they are to function with any reasonable efficiency. Otherwise, the electrodes will be coated with the particulate matter which has been removed from the air or other gas circulating through the precipitator and will no longer attract the particulate matter with any reasonable degree of efficiency.
A common way to clean the electrodes is to provide rappers wich are mechanically connected with one or more electrodes. While the precipitator is in operation, each rapper is intermittently operated to vibrate an electrode or electrodes thus causing the accumulated particulate matter to drop off. Each rapper is conventionally composed of a solenoid coil encircling a core which strikes an anvil when the solenoid is energized. The anvil is mechanically connected with one or more electrodes which are vibrated when the anvil is struck by the core.
Rectified AC current is conventionally used as current to energize the rappers. To efficiently clean the electrodes, the rappers have to be energized at an amplitude and for a period of time which will provide efficient cleaning. The electrodes become coated with several layers of particulate matter and if vibrated too severely by the rappers, will release all of the particulate matter. If all of the particulate matter from a particular electrode is released, an excessive quantity of matter will be in the stream of gas moving through the precipitator and will not be entirely removed before leaving the precipitator.
It has been found that if an electrode is cleaned by vibrating it properly, it is possible to cause the layer of particles in contact with the electrode to drop down while the layers of matter farther away from the electrode move toward the electrode to take the place of the particles which have dropped. Very few, if any particles will be released to the gas stream and therefore, the precipitator will not lose particles to the gas moving through it.
In the past some difficulty has been encountered in providing the control of current used to actuate the precipitators. Control systems previously used did not always energize each rapper for a period which will provide for efficient cleaning of the electrodes or frequently enough to ensure that the electrodes are sufficiently cleaned to efficiently remove particulate matter from the gases being treated by the precipitator.